Integrated circuits typically include a thin chip of silicon, which is formed by dicing a wafer. Each integrated circuit includes a plurality of input/output pads or the like that are formed on the silicon wafer. In order to assess the operational integrity and other characteristics of the wafer prior to dicing, the silicon wafer is subjected to testing to identify defective circuits.
Known apparatuses for testing silicon wafers include a test controller, which generates integrity test signals, and a probe card, which forms an electrical interface between the test controller and a silicon wafer under test by the apparatus. Known, probe cards typically include three major components: (1) an array of test probes; (2) a space transformer; and (3) a printed circuit board (“PCB”). The test probes, which are typically elongated, are arranged for contact with the input/output pads defined by the silicon wafer under test by the apparatus. The space transformer is respectively connected at opposite sides to the test probes and to the PCB, and converts the relatively high density spacing associated with the array of probes to a relatively low density spacing of electrical connections of the PCB.
Exemplary known test apparatuses include probes referred to as “vertical” or “cantilever” probes, depending on the manner in which the probes are supported and loaded. Referring to FIG. 1, there is shown a prior probe assembly 10 having “vertical” probes 12. Probe assembly 10 includes first and second plates 14, 16 maintained in spaced relation with respect to each other. Each of probes 12 of vertical probe assembly 10 is secured at first end 18 to first plate 14 and is received at second end 20 of probe 12 through opening 22 in second plate 16. As shown, the portions of each probe 12 adjacent first and second ends 18, 20 are oriented substantially parallel to the vertical movement direction for probe assembly 10, which is shown in FIG. 1 by arrows 24.
Because of the vertical orientation of the ends 18, 20 of probes 12, loads will be applied substantially axially at the second end 20 of each probe 12 upon contact with a device under test (DUT), and will be reacted substantially axially at first end 18. In this manner, probes 12 function like vertically-oriented column structures. Unlike typical column structures, however, vertical probes 12 are not straight and, instead, include curved intermediate portion 26 such that first and second ends 18, 20 of each of probes 12 are offset from each other. This construction facilitates deflection of probes 12 for predictable response of probes 12 when they are loaded upon contact with a device under test.
Referring to FIG. 2, there is shown prior probe assembly 28 having “cantilever” probes 30. As shown, each of probes 30 is secured at first end 32 to probe support plate 34. Each of probes 30 includes second end 36 that is V-shaped to define a point adapted for contact with a device under test. In contrast to probes 12 of FIG. 1 having ends 18, 20 parallel to the vertical movement of probe assembly 10, each of probes 30 is oriented substantially perpendicular to the vertical movement of probe assembly 28, identified in FIG. 2 by arrows 38. As a result, loading will be applied transversely to each probe 30 upon contact between second end 36 of probe 30 and a device under test. In this manner, probes 30 function like cantilever beam structures. The cantilever construction of probes 30 greatly facilitates deflection of the probes upon contact with a device under test.